The New York Fire Department said it treated three patients who were then taken to a hospital for what it considered minor injuries. The identities of the patients were not revealed.

U.S. President Donald Trump’s daughter-in-law Vanessa Trump, 40, opened the letter addressed to the president’s son Monday morning at her mother’s apartment, investigators said. She called 911 and said she was coughing and felt nauseous, police said.

The Trump Organization didn’t immediately respond to a request for comment.

Mail is collected across the street from 405 E. 54th street, where Donald Trump Jr.’s wife, Vanessa Trump, opened a letter containing white powder in New York on Monday. (Caitlin Ochs/Reuters)

“The Secret Service and our law enforcement partners in New York City are investigating a suspicious package addressed to one of our protectees received today in New York, New York. This is an active investigation and we cannot comment any further,” Secret Service special agent Jeffrey Adams said in a statement.

Vanessa Trump, a former model, and Donald Trump Jr. have five children, none of whom were home at the time of the incident.

Later on Monday, Trump Jr. tweeted his wife and children “are safe and unharmed after the incredibly scary situation that occurred this morning.”

White House spokesperson Sarah Huckabee Sanders said Monday that the president spoke by phone to Vanessa Trump about the incident.

Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning. Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior.

In March 2016, police detectives and FBI agents investigated a threatening letter sent to the Manhattan apartment of the president’s middle son, Eric, that also contained a white powder that turned out to be harmless. Envelopes containing white powder were also sent to Trump Tower, which served as the senior Trump’s campaign headquarters, twice in 2016.

Hoax attacks using white powder play on fears that date to 2001, when letters containing deadly anthrax were mailed to news organizations and the offices of two U.S. senators. Those letters killed five people.

A U.S. military scientist committed suicide in 2008 as federal prosecutors readied an indictment alleging he mailed the anthrax-laced letters.